Late Oligocene bunch grassland and early Miocene sod grassland ...€¦ · different times. Cursoriality appears in the North American fossil mammal record by early Oligocene (33

www.elsevier.com/locate/palaeo

Palaeogeography, Palaeoclimatology, Palaeoecology 207 (2004) 203–237

Late Oligocene bunch grassland and early Miocene sod grassland

paleosols from central Oregon, USA

Gregory J. Retallack*

Department of Geological Sciences, University of Oregon, Eugene, OR 97403-1272, USA

Received 4 March 2002; accepted 25 September 2003

Abstract

Fossil soils, burrows and mammals of the upper John Day Formation in central Oregon are evidence of bunch grasses and

open, semiarid vegetation as old as late Oligocene (earliest Arikareean, 30 Ma). Root traces in these paleosols include both

stout, tapering tubes, like roots of trees, as well as sinuous filamentous tubes, similar to roots of grasses. Paleosol structure is

fine subangular blocky, with patchy distribution of grass-like roots, as in wooded grassland and sagebrush steppe with bunch

grasses. Cursoriality in horses (Mesohippus, Miohippus) and hypsodonty in rhinos (Diceratherium) is also evidence for open

grassy vegetation. Trace fossils of Pallichnus (dung beetle boli) and Edaphichnium (earthworm chimneys) are characteristic of

wooded grassland paleosols, whereas Taenidium (cicada burrows) dominates desert shrubland paleosols, as has also been found

in Quaternary paleosols and soils of eastern Washington. In both Oligocene and Quaternary paleosol sequences, arid shrubland

and semiarid grassland paleosols alternate on Milankovitch frequencies (23, 41, 100 ka).

The oldest known paleosols in Oregon with crumb structure and abundant fine fossil root traces characteristic of sod

grasslands are dated by mammalian biostratigraphy as Hemingfordian (early Miocene, ca. 19 Ma). Wooded grassland habitats

are indicated by scattered chalcedony-calcite rhizoconcretions from large woody plants, and by fossil chalicotheres (Moropus),

camels (Gentilicamelus, ‘‘Paratylopus’’) and horses (Parahippus). Silty texture and silcrete horizons are evidence of semiarid to

arid paleoclimate, and are in striking contrast to highly calcareous, and clayey underlying paleosols of the John Day Formation.

These silcrete paleosols may represent the Miocene onset of summer-dry (Mediterranean) seasonality, as opposed to a summer-

wet (monsoonal) pattern of seasonality found in this region during the Oligocene.

Oregon’s early rangelands can be compared with those in the North American Great Plains. Granular-structured calcareous

paleosols of the Brule Formation of South Dakota are evidence of dry, bunch grasslands as old as 33 Ma (early Orellan, early

Oligocene), and crumb-structured paleosols of the Anderson Ranch Formation of Nebraska are evidence of sod grasslands as

old as 19 Ma (late Arikareean, early Miocene). Although grasses were a conspicuous part of dry rangelands well back into the

Oligocene, early and middle Miocene sod grasslands in North America were restricted to regions estimated to have had less

than 400 mm mean annual precipitation.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Grassland; Paleosol; Trace fossil; Fossil mammal; Oligocene; Miocene

0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.palaeo.2003.09.027

* Tel.: +1-541-3464558; fax: +1-541-3464692.

E-mail address: [email protected] (G.J. Retallack).

1. Introduction

The antiquity of grasslands has been of interest

ever since Darwin (1872) suggested its role in

G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 207 (2004) 203–237204

human evolution and since Kowalevsky (1873)

demonstrated the profound influence of grasslands

on the evolution of horses and other ungulates.

Mammalian hypsodonty is still regarded as an

adaptation to abrasiveness of grassy diet and mam-

malian cursorality as an adaptation to open vegeta-

tion (Janis, 2000; Janis et al., 2002), but various

components of grasslands ecosystems evolved at

different times. Cursoriality appears in the North

American fossil mammal record by early Oligocene

(33 Ma), and hypsodonty by early Miocene (18

Ma), but large, highly hypsodont, fully cursorial

horses do not appear until late Miocene (7 Ma:

MacFadden, 2000). Molecular clock studies of ar-

tiodactyl digestive RNases indicate an origin for

ruminant grass-digesting enzymes in the late Eocene

to early Oligocene (Jermann et al., 1995). Micro-

wear studies indicate a significant intake of grass by

Oligocene horses, but some Miocene horses were

true grazers (Solounias and Semprebon, 2002).

Isotopic studies of Miocene fossil grasses and

hypsodont mammals indicate that most grasses in

tropical regions then were C3 plants, as is typical

today only of high latitude and high altitude

grasses, and of most trees and shrubs (Koch,

1998; MacFadden, 2000). Carbon isotopic compo-

sition of fossil tooth enamel and paleosol carbonate

nodules indicate small amounts (20%) of C4 grasses

or CAM plants at least from the mid-Oligocene (29

Ma: Retallack, 2002a; Fox and Koch, 2003), and

perhaps earlier (Wang and Cerling, 1994), but a

marked late Miocene–Pliocene (7–2.5 Ma) increase

in abundance of C4 grasses throughout tropical

regions (Cerling et al., 1997; Fox and Koch,

2003, this volume). The fossil record of grass

leaves, anthoecia, pollen and phytoliths reveal

grasses well back into the Eocene, but widespread

taxa of open grasslands no earlier than late Oligo-

cene (Dugas and Retallack, 1993; Morley and

Richards, 1993; Jacobs et al., 1999; Stromberg,

2002, this volume). Another record of past grass-

lands with high temporal resolution is now becom-

ing available from the study of paleosols which

reveal for the Great Plains of North America a

three-stage evolution of Oligocene (33 Ma) desert

bunch grasslands, early Miocene (19 Ma) short sod

grasslands and late Miocene (7 Ma) tall sod grass-

lands (Retallack, 1997a, 2001a; Retallack et al.,

2002; with revised dating by MacFadden and Hunt,

1998). This study documents the paleosol record of

late Oligocene bunch grassland and early Miocene

sod grassland ecosystems in central Oregon (Figs. 1

and 2).

Paleosols of sod grasslands have abundant, fila-

mentous (less than 2 mm diameter), fossil root holes

and common, rounded pellets of earthworms and

other crumb peds. Soils with organically bound,

stable structure and elevated organic content for at

least 25 cm thickness are segregated as Mollisols in

the US soil taxonomy (Soil Survey Staff, 1999) or as

Chernozems in the FAO (1974) and other classifica-

tions (Stace et al., 1968). Soil organic matter, actual

roots and other body fossils of grasses are seldom

preserved in grassland paleosols because grasslands,

as opposed to marshes and fens, are well drained and

oxidized, allowing organic matter decay even after

burial (Retallack, 1998). Plant opal (phytoliths) accu-

mulates in soils and is locally abundant in paleosols

as an additional line of evidence for grasses (Strom-

berg, 2002, this volume), but the distinction between

sod and bunch grassland is not easily inferred from

phytoliths. Nor is this distinction apparent from

carbon isotopic detection of C4 grasses, which form

both sod and bunch grasslands in regions with warm

growing season. Furthermore, C4 grasses never

spread into Oregon (Cerling et al., 1997). Other trace

fossils in paleosols indicative of grasslands include

the chimneys and fecal pellets of earthworms (Eda-

aphichnium) and the boli and clayey shells of dung

beetles (Pallichnus, Coprinisphaera: Retallack, 1990;

Duringer et al., 2000; Genise et al., 2000). Earthworm

fecal pellets in grassland paleosols are more common

than isolated chimneys and burrow fills. They dom-

inate the very fabric of grassland soils, which have, in

effect, been through the guts of earthworms many

times (Darwin, 1896). European earthworms are es-

pecially well known in this respect and have been

widely exported for pasture improvement, but native

earthworms of the New World, Asia and Australia

also have comparable effects on soils (Joshi and

Kelkar, 1952; Barley, 1959; Pawluk and Bal, 1985).

These small 2–5 mm ellipsoidal fecal pellets are also

comparable in size to the spacing of lateral rootlets on

the filamentous roots of grasses (Weaver, 1920). Both

grass roots and earthworms create in soils of sod

grasslands a characteristic crumb ped structure, which

Fig. 1. Geological sequence and selected mammal fossils from the upper John Day Formation, near Kimberly, central Oregon (fossil illustrations

after Sinclair, 1905; Osborn, 1918; Lull, 1921; Schultz and Falkenbach, 1947, 1949, 1968; Rensberger, 1971, 1983; Wang, 1994; Wang et al.,

1999; Bryant, 1996; Prothero, 1996; Lander, 1998). Stippled portions of skulls are reconstructed, rather than preserved.

G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 207 (2004) 203–237 205

is commonly preserved in paleosols (Retallack,

1997a,b, 2001a). Other features of paleosols such as

silcretes, calcareous nodules, chemical composition

and grain size are indications of former climate,

sedimentary setting, parent materials and duration of

soil formation (Retallack, 2001b), and reveal the

evolutionary and environmental context of early

grassland ecosystems.

Fig. 2. Geological map and cross-section of Longview Ranch, south of Kimberly, central Oregon.



2. Materials and methods

2.1. Field and laboratory approaches

This research focused on measurement of detailed

stratigraphic sections documenting every paleosol and

its environmentally sensitive features in the late Oligo-

cene to early Miocene upper John Day Formation near

Kimberly and Spray, central Oregon (Figs. 1 and 2). All

paleosols were logged using eye-heights at locations

chosen so that a composite section could be assembled

from the correlation of volcanic ash and other marker

beds in three separate areas on Longview Ranch (Figs.

2–5) and four additional areas around Kimberly and

Spray (Figs. 2, 6–8). Field measures taken were

Fig. 3. Longview Ranch Airport section: a measured section showing d

(reaction with 0.1 N HCl scale of Retallack, 1997b) and Munsell hue of p

the badlands 1 km west of Longview Ranch airport (N44.663814j E119.66

Fossil beds national Monument, Kimberly, Oregon (catalog online http://w

reaction with dilute acid (1.2 M HCl), Munsell color,

depth to carbonate and assessment of the degree of

development of the paleosols from carbonate nodule

size and abundance, and from destruction of relict

bedding (Retallack, 1997b). Selected profiles and

specimens were analyzed for major oxides and trace

elements by Bondar Clegg Inc of Vancouver BC

(Appendix A), and selected molar weathering ratios

were calculated (Retallack, 1997b). Carbonate nodules

were analyzed for few of the paleosols, because this

study aimed to quantify non-calcic hydrolysis. Petro-

graphic thin sections were counted for 500 points in

separate counts for mineral composition and grain size

using a Swift automatic counter (Retallack, 2002a),

with precision of about 2% (Murphy, 1983). These data

egree of development (scale of Retallack, 1997b), calcareousness

aleosols of the middle Turtle Cove Member, John Day Formation in

659j). JODA numbers refer to rock specimens curated at John Day

ww.museum.nps.gov).

http:\\www.museum.nps.gov


Fig. 4. Roundup Flat section: a measured section of paleosols of the upper Turtle Cove Member of the John Day Formation in the prominent

badlands 2 km northeast of Longview Ranch (N44.692465j E119.638896j). The lithological key and conventions are as for Fig. 3.


Fig. 5. Bone Creek Section: a measured section of paleosols of the uppermost Turtle Cove and Kimberly Members and Hemingfordian beds of

the John Day Formation in gullies high within the headwaters of Bone Creek, 3 km northeast of Longview Ranch (N44.700229jE119.624658j). Lithological key and conventions are as for Fig. 3. Meter levels of the upper portion of this section are estimated from a

regional composite stratigraphic section including strata missing in an erosional disconformity here.


supplement comparable data published elsewhere

(Retallack et al., 2000). Descriptive terminology of

the paleosols is after Brewer (1976) and Soil Survey

Staff (1993). Rocks and fossils collected as a part of this

work are curated at the John Day Fossil Beds National

Monument, Kimberly (catalog online at http://

www.museum.nps.gov).

2.2. Stratigraphic setting

The upper John Day Formation in the John Day

Valley of central Oregon is well known for fossil

mammals ranging in age from early Oligocene (frag-

mentary Orellan North American Land Mammal Age

or NALMA, entelodons only) to early Miocene

(Hemingfordian NALMA: Fremd et al., 1994; Orr

and Orr, 1998; Coombs et al., 2001; Hunt and Step-

leton, 2001). The upper Turtle Cove, Kimberly and

lower Haystack Valley Members yield mammal fos-

sils of the Arikareean NALMA (Fig. 9), and include

the ‘Monroecreekian’ (29.5–25.8 Ma) and ‘Harriso-

nian’ (25.8–23.5) subdivisions of Alroy (2000). The

age of the lower part of the sequence is well con-

strained by four 40Ar/39Ar single-crystal laser-fusion


Fig. 6. Kimberly Section: a measured section of paleosols of the

upper Kimberly Member of the John Day Formation in cliffs beside

the road to Monument 1 km northeast of Kimberly (N44.776600jE119.630734j). The lithological key and conventions are as for

Fig. 3.


radiometric ages on tuffs (by Swisher for Fremd et al.,

1994), and by magnetostratigraphic chrons (Prothero

and Rensberger, 1985; Albright et al., 2001), adjusted

to the revised time scale of Cande and Kent (1992).

The radiometric ages allow interpolation of geological

age for the lower part of the sequence (black dots and

regression line of Fig. 9), and give results not much

different from the magnetostratigraphic chrons (also

plotted in gray on Fig. 9). Dating of the upper part of

the section is an extrapolation, supported by biostrati-

graphic correlations with Nebraska and one problem-

atic radiometric age determination (Coombs et al.,

2001).

Measured sections at Longview Ranch airport (Fig.

3), Roundup Flat (Fig. 4) and Bone Creek (Fig. 5)

were correlated by means of the Deep Creek, Tin Roof

and other marker tuffs (Fremd et al., 1994). They are

also zoned biostratigraphically (Fig. 10), as the

‘‘Promerycochoerus’’ beds of Merriam and Sinclair

(1906), and several rodent zones of Meniscomys,

Pleurolicus and Entoptychus (Rensberger, 1971,

1973, 1983). The Kimberly Member, with Entopty-

chus planifrons at its base and Entoptychus individens

at its top, is a distinctive loessic sequence of paleosols

(Fig. 5) mappable from Bone Creek north to Kimberly

(Fig. 6). The basal Haystack Creek Member near

Balm Creek and Spray contains latest Arikareean

mammals such as E. individens and Merychyus are-

narum, and in the uppermost part of the exposures a

tuff identified as the ATR tuff (Fig. 7). This tuff has

been dated at Black Bone Hill (Fig. 8) as 22.6 Ma,

which is an average of ages ranging from 24.4 to 19.6

Ma (Coombs et al., 2001). The tuff is redeposited and

uncracked by soil formation, so that recycling of older

grains is more likely than intrusion of younger grains.

Other considerations favoring the youngest age

includes paleomagnetic and radiometric dating of

the basal Hemingfordian in Nebraska (MacFadden

and Hunt, 1998), because the tuff at Black Bone Hill

is 12 m above sites there for early Hemingfordian

rodents Schizodontomys greeni and Mylagaulodon

angulatus (Rensberger, 1973), as well as other mam-

mals such as ‘‘Paratylopus’’ cameloides (Fremd et al.,

1994; Honey et al., 1998). Overlying strata of the

Johnson Creek and Bone Creek sections contain later

Hemingfordian fossils including Moropus oregonen-

sis, Daphaenodon sp., Gentilicamelus sternbergi and

Parahippus sp. (Merriam and Sinclair, 1906; Wood-

burne and Robinson, 1977; Dingus, 1990; Honey et

al., 1998; Lander, 1998; MacFadden, 1998; Hunt and

Stepleton, 2001). This uppermost unit of the John

Day Formation is unconformably overlain by basal-

tic sandstones and peaty paleosols of an unnamed

unit with middle Miocene plant fossils, in turn,

overlain by middle Miocene (16 Ma) Columbia

River Basalt Group (Fisher and Rensberger, 1972).

Disconformities due to paleovalley incision at the

bottom and top of the Hemingfordian beds in upper

Bone Creek (Fig. 5) have paleotopographic relief

within the mapped area (Fig. 2) of at least 50 and

77 m, respectively. The lower disconformity was


Fig. 7. Balm Creek Section: a measured section of paleosols of the lower Haystack Valley Member of the John Day Formation in badlands

behind the house of Cal and Nina Hopper, east of Balm Creek, 3 km east of Spray (N44.837629j E119.740380j). The lithological key and

conventions are as for Fig. 3.


Fig. 8. Black Bone Hill and Johnson Creek Sections: a measured section of paleosols of the middle and upper Haystack Valley Member of the

John Day Formation in a conical white hill west of the John Day River 1 km south of Kimberly (N44.74053j E119.647158j) and in cliffs north

of the farm road into the canyon of Johnson Creek 1 km west of Kimberly (N44.752470j E119.654222j). The lithological key and conventionsare as for Fig. 3.


filled by basal conglomerates with paleocurrents

indicating that the paleovalley drained to the north-

west, which is the same direction as flow within

the much broader depositional basin of the Turtle

Cove Member (Fig. 11).

2.3. Alterations after burial

Diagenetic alterations of paleosols of the John Day

Formation have been discussed at length elsewhere

(Retallack et al., 2000) and include burial gleization,

Fig. 9. Graphic correlation and regression of new 39Ar/40Ar ages (black circles) for tuffs in the upper John Day Formation on Longview Ranch

(Fremd et al., 1994). Also shown (gray text) are magnetostratigraphic chrons (C10.2R to C7.2R after Prothero and Rensberger, 1985), and North

American Land Mammal ‘‘Ages’’ (NALMA of Alroy, 2000), and rodent biostratigraphy of Rensberger (1971, 1973, 1983). The youngest of the

averaged dates for the ATR tuff is most consistent with underlying Hemingfordian fossils (Coombs et al., 2001) and extrapolation from well-

dated older rocks. The upper part of the succession is primarily dated by biostratigraphy.


celadonitization, zeolitization and burial compaction.

The striking green color of the Turtle Cove Member

and basal Haystack Valley Member in Balm Creek is

from celadonite and clinoptilolite formed by Ostwald

ripening of imogolite and illite during the early

Miocene (Hay, 1963). Both the calcareous nodules

and some paleosols (Yapas and Yapaspa pedotypes of

Table 1) preserve light brown to gray colors that are

probably close to original colors of the soils. The

Kimberly Member and Hemingfordian parts of the

Haystack Valley member are unzeolitized and unce-

ladonitized (Hay, 1963), and their volcanic shards still

glassy, so these paleosols also are more like the

original soils. Lack of compactional deformation of

volcanic shards in all these paleosols supports use of

physical constants for Inceptisols in calculating burial

compaction (Sheldon and Retallack, 2001).

3. Paleosol classification and its implications

3.1. Approaches to paleosol classitication

Paleosols of the upper John Day Formation are

here classified using two quite different kinds of units:

(1) field pedotypes and (2) taxonomic units. Pedo-

Fig. 10. Stratigraphic range of fossils collected during this study (all specimens curated in collections of John Day Fossil Beds National

Monument: catalog online at http://www.museum.nps.gov).

Fig. 11. Paleocurrents in the Turtle Cove Member and Hemingfordian beds of the John Day Formation.



Table 1

Inferred classification of reconstructed paleosols in the upper John Day Formation and lowermost Columbia River Basalt Group on Longview

Ranch, central Oregon

Pedotype Meaning Type profile Field diagnosis US taxonomy FAO map Australian Northcote

key

Abiaxi Bitter root Bone Creek

(299.0 m)

Chalcedony rhizoconcretions

in high-soda clayey sandstone

with relict bedding

Xerept Eutric

Cambisol

Brown clay Uc1.21

Cmti (2) New Mascall Ranch Brown siltstone with

relict bedding and root traces

Fluvent Eutric

Fluvisol

Alluvial soil Um1.21

Micay (1) Root Clarno mammal

quarry

Brown to olive clay with

root traces and relict bedding

Aquandic

Fluvaquent

Eutric

Fluvisol

Alluvial soil Uf1.41

Iscit Path Bone Creek

(310.0 m)

Crumb-structured surface

(A) over thick siliceous

duripan (Bq)

Durixeroll Mollic

Solonchak

Brown

hardpan

soil

Um6.22

Monana Underneath Bone Creek

(317.3 m)

Clayey lignite (O) over

basaltic sandstone (A)

Saprist Histosol Acid peat O

Patu Mountain Bone Creek

(302.4 m)

Crumb structured surface

(A) over shallow ( < 50 cm)

micrite-chalcedony

rhizoconcretions (Bk)

Xeroll Kastan-ozem Cherno-zem Um6.22

Plas White Bone Creek

(275.5 m)

Silty white surface (A) with

calcareous nodules

(Bk)>45 cm deep

Typic

Haplocalcid

Calcic

Xerosol

Gray-brown

calcareous soil

Gc1.21

Plaspa In white Bone Creek

(275.8 m)

Silty white surface (A) with

calcareous nodules

(Bk) < 45 cm deep

Ustic

Haplocalcid

Calcic

Yermisol

Gray-brown

calcareous soil

Gc1.12

Tima Write Bone Creek

(314.0 m)

Granular structured surface

(A) over clayey subsurface (Bt)

and siliceous duripan (Bq)

Natric

Durixeralf

Mollic

Solonetz

Solonetz Dy4.13

Yapas (1) Grease Carroll Rim Dark brown, fine blocky peds

(A, Bw), calcareous nodules

(Bk)>50 cm deep

Haplustand Mollic

Andosol

Prairie soil Gc2.21

Yapaspa In grease Bone Creek

(231.0 m)

Dark brown, fine blocky peds


(Bk) < 50 cm deep

Vitrandic

Haplocalcid

Calcic

Xerosol

Gray-brown

calcareous soil

Gc2.12

Xaxus (1) Green Foree Green, fine blocky peds


(Bk)>50 cm deep

Aquic

Ustivitrand

Vitric

Andosol

Wiesen-boden Gc1.21

Xaxuspa In green Foree

(250 m)

Green, fine blocky peds

(A, Bw), calcareous

nodules (Bk) < 50 cm deep

Aquic

Haplo-calcid

Calcaric

Gleysol

Gray-brown

calcareous soil

Gc1.12

Sahaptin meaning is after Rigsby (1965) and DeLancey et al. (1988): type profiles of most paleosols are described here, and the others are

described by (1) Retallack et al. (2000), and (2) Retallack et al. (2002).


types are a non-genetic field mapping designation

(Retallack, 1994a), comparable to soil series (Soil

Survey Staff, 1993). These named pedotypes (Table

1) are part of a wider scheme of field mapping

categories for paleosols in the John Day Formation

(Retallack et al., 2000), using simple descriptive terms

from the Sahaptin Native American language (Rigsby,

1965; DeLancey et al., 1988). Selected profiles of

each pedotype not described elsewhere (Retallack et

al., 2000) are characterized chemically and petro-

graphically here (Table 2; Figs. 12–15). The Monana

pedotype, logged and characterized during this study

(Table 1; Fig. 5) is one of a variety of paleosols

associated with the middle Miocene, Columbia River

Basalt Group, rather than the John Day Formation.

Paleosols of the John Day Formation formerly

regarded as shallow-calcic variants of Xaxus, Yapas

and Plas pedotypes (Retallack et al., 2000) are here

Table 2

Type sections of newly proposed pedotypes in upper Bone Creek section (Fig. 4) and Foree section (Xaxuspa only)

Paleosol Level A horizon B horizon C horizon

Type

Abiaxi

loam

299.0 m 0 cm, A, medium-grained

sandstone, pale yellow

(5Y7/3) with mottles up to

1 cm of light yellowish brown

(2.5Y6/3); root traces woody

and up to 3 mm diameter,

replaced by chalcedony of

white (5Y8/1) and clay of

brown; non-calcareous;

intertextic insepic microfabric,

with common volcanic rock

fragments

Not present � 68 cm, C, medium-grained

sandstone light brownish gray

(2.5Y6/3), with stringers of

ripple-marked silty sandstone,

white (5Y8/1); claystone clasts

up to 5 mm of pale brown

(10YR6/3); intertextic insepic

microfabric, with common

volcanic rock fragments

Type

Iscit

clay

310.0 m 0 cm, A, siltstone, light

yellowish brown (2.5Y6/4);

crumb peds with abundant

fine (1–2 mm) root traces,

and scattered large root traces

(6–7 mm) of pale yellow

(2.5Y8/2); non-calcareous;

scattered clasts up to 4 mm

of pale yellow (2.5Y8/2) and

light olive brown (2.5Y5/6);

pyrolusite dendrites black

(5Y2.5/); insepic

agglomeroplasmic, with

rounded and coated grains

� 15 cm, By, silicified medium-

grained sandstone, light olive

brown (2.5Y5/4), with mottles

of pale yellow (2.5Y7/4), clay

skins of grayish brown

(2.5Y5/2), and granules of white

(2.5Y8/1) and pale yellow

(2.5Y8/3); scattered mangans

(dark gray (2.5Y4/1); non-

calcareous; insepic

agglomeroplasmic, with

rounded and coated grains

� 45 cm (A horizon of Patu

paleosol), light olive brown

(2.5Y5/3), crumb peds, outlined

by argillans of grayish brown

(2.5Y5/2); root traces mostly fine

(1 mm) but one was 8 cm

diameter at a depth of 30 cm and

expanded to 13 cm diameter at

the surface; rare burrows 3 cm

diameter filled with pale yellow

(2.5Y7/3) sandstone; insepic

intertextic

Type

Patu

clay

loam

302.4 m 0 cm, A, siltstone, light

yellowish brown (2.5Y6/3),

crumb peds defined by

argillans light olive brown

(2.5Y5/3), abundant fine

(1 mm) root traces of light

olive brown (2.5Y5/3) and

scattered large (4 mm)

chalcedony rhizoconcretions

of white (5Y8/1); scattered

pyrolusite dendrites black

(5Y2.5/1); non-calcareous;

porphyroskelic skelmosepic,

with concentrically banded

rhizoconcretions

� 32 cm, Bk, sandy siltstone,

pale yellow (2.5Y7/3); weakly

calcareous chalcedony

rhizoconcretions of white

(2.5Y8/1); few burrows 1.5 cm

diameter of white (2.5Y8/1)

sand; porphyroskelic mosepic in

matrix, and calciasepic to insepic

in banded rhizoconcretions

� 41 cm, C, tuffaceous medium-

grained sandstone, white (5Y8/1);

non-calcareous, relict planar

bedding; few large strata-concordant

root traces 7 mm diameter

of pale olive (5Y6/3) claystone;

insepic agglomeroplasmic, with

common rounded and coated soil

granules

Type

Plas

clay

275.5 m 0 cm, A, clayey fine-grained

sandstone, pale yellow

(2.5Y7/3), non-calcareous;

grains of white (2.5Y8/1) and

olive gray (5Y4/2); abundant

fine (1–2 mm) root traces of

light olive brown (2.5Y3/3);

insepic agglomeroplasmic

microfabric, with common

volcanic rock fragments and

few shards

� 62 cm, Bw, clayey fine-

grained sandstone, light yellowish

brown (2.5Y6/3); massive, non-

calcareous; intertextic insepic

� 94 cm, Bk, large (up to 25 cm)

calcareous nodules and ledges,

gray (5Y5/1); moderately

calcareous; few slickensided

mangans very dark gray (5Y3/1);

intertextic calciasepic

� 118 cm (A horizon of Plaspa

paleosol), clayey, fine –grained

tuffaceous sandstone, pale yellow

(2.5Y7/3), with root traces up

to 4 mm diameter of light olive

brown (2.5Y5/3); non-calcareous;

agglomero-plasmic insepic

microfabric


Table 2 (continued )

Paleosol Level A horizon B horizon C horizon

Type

Plaspa

clay

loam


tuffaceous sandstone, pale

yellow (2.5Y7/3); with root

traces up to 6 mm diameter of

light olive brown (2.5Y5/3)

and near-vertical burrow

2.4 cm diameter extending

down 16 cm from surface;

non-calcareous; porphyroskelic

insepic, with common volcanic

shards and rock fragments

� 11 cm, AB, fine grained

sandstone, light

yellowish brown (2.5Y6/3); root

traces and burrow as above

� 30 cm, Bk, calcareous nodules,

gray (5Y5/1), up to 15 cm

diameter, outermost 1 mm

weathering rind of pale yellow

(2.5Y7/3), then a 2 mm rind of

olive brown (2.5Y4/3), then a 2

mm rind of dark gray (5Y4/1) ;

moderately calcareous;

agglomeroplasmic calciasepic

� 45 cm (A horizon of type Plas

paleosol) clayey fine-grained

sandstone, pale yellow (2.5Y7/3),

non-calcareous; grains of white

(2.5Y8/1) and olive gray (5Y4/2);

abundant fine (1–2 mm) root traces

of light olive brown (2.5Y3/3);

insepic agglomeroplasmic

microfabric, with common volcanic

rock fragments and few shards

Type

Tima

clay


sandstone, pale brown

(10YR6/3), with common

drab-haloed root traces, up to

4 cm diameter of white

(5Y8/1) and haloes of light

gray (5Y7/2); non-calcareous;

granular to fine blocky peds;

agglomeroplasmic insepic, with

rounded and coated granules

� 22 cm, Bt, clayey siltstone,

yellowish brown (10YR5/4);

non-calcareous; granular to fine

blocky peds; common drab-haloed

root traces as above;

agglomeroplasmic insepic

microfabric, with rounded and

coated granules

� 58 cm, C, clayey fine-grained

sandstone, light gray (5Y7/2), with

granules of pale yellow (5Y8/2)

and scattered fine root traces

of pale yellow (5Y8/4); non-

calcareous: agglomeroplasmic

insepic

� 90 cm, Cy, silcrete, light gray

(5Y7/2); non-calcareous;

agglomeroplasmic insepic with

pockets of banded chalcedony

Type

Yapaspa

clay

231.0 m 0 cm, A, clayey siltstone,

light yellowish brown

(2.5Y6/3): granular to fine

blocky peds; common fine

(1–2 mm) root traces; granular

to fine blocky peds; very

weakly calcareous

� 37 cm, Bk, siltstone, with

abundant pale yellow (2.5Y7/3),

rounded and scattered calcareous

nodules up to 4 cm; moderately

calcareous

� 45 cm (A horizon of Yapas

paleosol on white tuffaceous marker

bed), clayey siltstone, grayish brown

(2.5Y5/2); granular to fine blocky

peds; very weakly calcareous

Type

Xaxuspa

clay

250 cm (see

Retallack et al.,

2000, Fig. 117)

0 cm, A, siltstone, grayish

green (5G5/2), weakly

calcareous with strongly

calcareous rhizoconcretions

from overlying tabular

micritic agglomeroplasmic

crystic layer; non-calcareous

matrix micofabric intertextic

skelmosepic common volcanic


� 36 cm, Bk, greenish gray

(5GY6/1), with common 5–6

cm diameter calcareous nodules

white (5Y8/2) with

agglomeroplasmic calciasepic

and crystic microfabric

� 86 cm, C, siltstone, greenish gray

(5GY6/1), weakly calcareous;

microfabric agglomeroplasmic

skelmosepic with common volcanic



separated as newly defined pedotypes Xaxuspa,

Yapaspa and Plaspa, using a Sahaptin postposition

for ‘‘in’’ or ‘‘at’’ (Sapir, 1911; Rigsby, 1965). These

shallow calcic paleosols represent different soils and

environments from otherwise similar paleosols with

deep calcic horizons.

Taxonomic units in contrast are part of a compre-

hensive classification of the US Soil Conservation

Service (Soil Survey Staff, 1999), which require

specific laboratory analyses, and are thus interpretive

for paleosols altered during burial (Retallack, 1993,

1997b). Proxy chemical and petrographic data are

needed to classify paleosols within this and other soil

classifications, such as that of the Food and Agricul-

ture Organization of UNESCO (FAO, 1974, 1975a,b)

and of the Australian Commonwealth Industrial and

Scientific Organization (Stace et al., 1968). One soil

classification does not require extensive interpretation

of proxies for paleosols, and this coded key of North-

cote (1974) has also been applied to the paleosols

Fig. 12. Detailed section of Iscit and Patu paleosols at 613.8–615.2 m in Bone Creek (Fig. 5). Molecular weathering ratios were chosen as

proxies of (from left to right), salinization, calcification, lessivage, base leaching, chemical leaching and gleization (following Retallack, 1997b).

Lithological key and other conventions are as for Fig. 3.


(Table 1). Like the paleosol classification of Mack et

al. (1993), the Northcote (1974) key does not yet lead

to useful paleosol interpretation, compared with better

known soil classifications.

3.2. Interpreted paleosol classification

Field pedotypes and their interpreted classification

within modern schemes designed for soils are shown

in Table 1. Newly proposed pedotypes are described

Fig. 13. Detailed section of Patu, Abiaxi and Cmti paleosols at 605.2–

in Table 2, and Table 3 outlines the interpreted

paleoenvironmnetal significance of each pedotype

and its fossils.

Many of the paleosols are dominated by volca-

nic shards and probably also had non-crystalline

colloids now recrystallized to clinoptolilite and cela-

donite (Retallack et al., 2000), as in Andisols (suffix

‘‘-and’’ of Soil Survey Staff, 1999) and Andosols

(FAO, 1974). Other paleosols have crumb structure,

fine root traces and thickness of crumb structure (at

607.3 m in Bone Creek (Fig. 5). Conventions are as for Fig. 12.

Fig. 14. Detailed section of Tima paleosol at 608.0–609.1 m in Bone Creek (Fig. 5). Conventions are as for Fig. 12.


least 25 cm) to qualify as Mollisols (suffix ‘‘-oll’’ of

Soil Survey Staff, 1999) and Kastanozems (of FAO,

1974). Other paleosols have high soda–potash ratios,

shallow nodules and concretions of calcite and chal-

cedony indicative of Aridisols (suffix ‘‘-id’’ of Soil

Survey Staff, 1999) and of Xerosols, Solonchak and

Solonetz (of FAO, 1974). Other paleosols are weakly

developed with bedding planes of sedimentary parent

material little disrupted by root traces as in Entisols

(suffix ‘‘-ent’’ of Soil Survey Staff, 1999) and Fluvi-

sols (FAO, 1974).

3.3. Paleoenvironmental implications of classification

A general concept of paleoenvironment can be

gained from taxonomic considerations, accepting the

identifications given in Table 1 and their supporting

proxies discussed above. For example, some of the

Fig. 15. Detailed section of Plaspa and Plas paleosols at 274.6–276

paleosols (Xaxus, Yapas, Micay) in the Turtle Cove

and lower Haystack Valley Members are taxonomi-

cally similar to the suite of soils now found near

Tehuacan, Mexico (map unit To2-2bc of FAO,

1975b). This intermontane basin within the central

Transmexican Volcanic Belt includes grassy decidu-

ous woodlands and bunch grassland (Retallack et al.,

2000). In contrast, other paleosols in the Turtle Cove

and lower Haystack Valley Members (Xaxuspa and

Yapaspa) are more like desert soils of the basins north

of Mexico City to Cerritos (map unit Xk7-2a of FAO,

1975b). These grassy woodland and desert shrubland

paleosols alternate through much of the Turtle Cove

and lower Haystack Valley Members, and comparable

alternation of white silty paleosols (Plas and Plaspa)

continues within the Kimberly Member.

Modern soilscapes taxonomically comparable with

Plas paleosols of the Kimberly and middle Haystack

.0 m in Bone Creek (Fig. 5). Conventions are as for Fig. 12.

Table 3

Interpreted paleoenvironment of paleosols of the upper John Day Formation

Pedotype Paleoclimate Former

vegetation

Former animals Paleotopography Parent

materials

Time for

formation

Abiaxi Insufficiently

developed

as an indicator

Saline scrub None found Salt pans Rhyodacitic

volcaniclastic

sand

0.01–0.1 ka

Cmti Insufficiently

developed

as an indicator

Early successional

riparian grassland

Horse (Parahippus),

camel (G. sternbergi),

chalicothere (Moropus

oregonensis), bear–dog

(Daphaenodon)

Dry silty

swales

in river

channels

Redeposited

rhyodacitic

silts and

sands

0.005–0.01 ka

Micay Insufficiently

developed

as an indicator

Early successional

riparian vegetation

None found River banks

and point

bars

Tuffaceous

fluvially

redeposited silts

and sands

0.005–0.01 ka

Iscit Semiarid

seasonally dry

Grassy woodland None found Floodplain Vitric-tuffaceous

siltstone

1–5 ka

Patu Semiarid (300–

400 mm mean

annual precipitation)

seasonally dry

Lightly wooded

short sod grassland

None found Floodplain Tuffaceous

siltstone

0.5–2 ka

Plas Semiarid (400–

500 mm mean


Sagebrush

shrubland

Horse (Miohippus) Floodplain Tuffaceous silts 2–7 ka

Plaspa Semiarid (300–

400 mm mean


Desert scrub Pocket gopher

(E. planifrons), mouse

deer (H. minutus)

Floodplain Tuffaceous silts 2–7 ka

Tima Semiarid, seasonally

dry

Dry woodland None found Floodplain Vitric tuffaceous

siltstone

2–7 ka

Yapas Subhumid (600–

1050 mm mean


seasonally dry

Open grassy

woodland and

wooded grassland

None found in this study

(but see Retallack et al.,

2000)

Well-drained

low relief

floodplain

Redeposited

rhyo-dacitic tuff

10–50 ka

Yapaspa Semiarid (350–

600 mm mean


Sagebrush

shrubland

None found Well-drained

low relief

floodplain

Redeposited

rhyodacitic

crystal tuff

10–50 ka

Xaxus Subhumid–semiarid

(500–850 mm mean


seasonally wet

Lightly wooded,

seasonally

wet meadow

Earthworms (Edaphichium),

dung beetles (Pallichnus),

termites (Termitichnus), snails

(Vespericola dalli, Monadenia

marginicola), pocket gophers

(Entoptychus spp), mouse deer

(Nanotragulus planiceps),

oreodonts (Merycochoerus superbus,

Eporeodon occidentalis, Merychyus

arenarum), rhinos (Diceratherium

sp.), horses (Miohippus–

Mesohippus spp.)

Seasonally

wet alluvial

lowland

Redeposied

rhyodacitic tuff

10–50 ka

Xaxuspa Semiarid (300–

500 mm mean


Sagebrush desert

grassland

Cicadas (Taenidium), snails

(‘‘Polygrya’’ expansa,

Monadenia dubiosa), pocket

gophers (Entoptychus spp.)

mouse deer (H. hesperius)

Seasonally wet

alluvial lowland

Redeposited

rhyodacitic tuff

10–50 ka



Valley Members are in the western Chihuahua Desert

of the Central Mexican Plateau from Moctezuma

north to Cuidad Camargo (map unit Xk6-2ab of

FAO, 1975b), but Plaspa paleosols are more like

soilscapes further north in Chihuahua near Salinal

(map unitYk9-2ab of FAO, 1975b). The desert shrub-

lands to the south have common yucca and saltbush,

but those to the north are sparser, and both lack the

large saguaro cactus that characterizes Sonoran desert

vegetation.

Paleosols of the upper Haystack Valley Member in

Johnson and Bone Creeks do not show repetitious

alternations, and resemble soils around Great Salt

Lake, Utah (map unit So1-3a of FAO, 1975a). This

is an intermontane basin of saltbush scrub and sage-

brush steppe, with local riparian woodland of cotton-

wood and willow.

4. Paleoenvironment interpreted from soil features

4.1. Paleoclimate

Two separate soil features can be used to infer

former mean annual precipitation from paleosols,

depth to carbonate and chemical composition. The

depth to carbonate (D, in cm) in paleosols is related to

precipitation (P, in mm) by the following equation

(Retallack, 1994b, 2000; Royer, 1999; Wynn and

Retallack, 2001):

P ¼ 139:6þ 6:388D� 0:01303D2

The paleosols measured had carbonate nodules or

carbonate-rich concretions (not wisps or thick contin-

uous layers) and were developed on unconsolidated

loess and alluvium (not bedrock) of an alluvial bot-

tomland (not hill slopes). These variables uncon-

strained would compromise the relationship between

depth to carbonate and precipitation (Royer, 1999;

Retallack, 2000). No correction was made for erosion

of paleosols because root traces and paleosol surfaces

did not appear disrupted, and because rates of sedi-

ment accumulation were unusually high (Fig. 9;

Retallack, 1998). No correction was made for atmo-

spheric CO2 levels either, because these have not been

shown to have been high or variable during the late

Oligocene or early Miocene (Retallack, 2002b). The

depth to carbonate was corrected for burial compac-

tion (using Inceptisol physical constants of Sheldon

and Retallack, 2001).

A second estimate of mean annual precipitation (P,

in mm) came from chemical index of alteration

without potassium (C, which is the molar ratio of

alumina over alumina plus soda, lime and magnesia

times 100) of paleosol subsurface (Bt or Bw) horizons

(Sheldon et al., 2002):

P ¼ 221:12e0:0197C

This estimate (open boxes in Fig. 16) did not seem

as sensitive to short episodes of desertification as the

depth to carbonate (black circles in Fig. 16) for three

reasons. First, degree of chemical weathering would

have been negligible and erosion of upland soils more

widespread during episodes of desertification (Best-

land, 2000). Second, this transfer function is calibrat-

ed for precipitation between 200 and 1600 per annum,

and not for higher or lower precipitation (Sheldon et

al., 2002). Third, the expense of chemical analysis did

not permit as many determinations as were made of

depth to carbonate. Nevertheless, both transfer func-

tions are in substantial agreement in indicating semi-

arid to arid conditions until about 19 Ma, then a

subsequent swing toward subhumid conditions.

Depth to carbonate and recurrent silty, loessial

facies indicate drier intervals at 25.8, 23.2, 21.1 and

19.2 Ma (Fig. 16). These times of aridity were global,

because coeval arid phases are seen in the North

American Great Plains (26 Ma Monroe Creek Forma-

tion, 23 Ma Rosebud Formation, 21 Ma Harrison

Formation and 19 Ma Anderson Ranch Formation:

Retallack, 1997a; Hunt, 2002), and also in deep-sea

cores, where arid phases correspond to glacial advan-

ces in Antarctica (Oi2 at 25 Ma and Mi1 at 23 Ma of

Zachos et al., 2001a,b). The terminal Oligocene

aridification is striking in outcrop, and the caliche

caprock north of Kimberly, is very similar to the

terminal Monroe Creek Formation caprock in Smiley

Canyon and elsewhere in Nebraska (Schultz and

Stout, 1981).

A remarkable feature of the paleoprecipitation

record from depth to carbonate (Fig. 16) is high

variability on Milankovitch temporal scales (103–

105 years), as has been noted before in the John

Day Formation (Bestland and Swisher, 1996). Each

Fig. 16. Milankovitch scale (41–100 ka) fluctuation (B, right, in portion of record) and broader trends of paleoprecipitation (A, left, for whole

record) inferred from depth to Bk horizons (open circles) and from chemical composition of Bt horizons (open squares) in the upper John Day

Formation near Kimberly and Spray. Chemical data are mainly for deep carbonate (more humid) paleosols of triplets like those of Fig. 17. Error

envelopes and bars (thin gray lines) are one standard error. Only the interval 28.5–23.5 is well dated radiometrically, with the younger part

extrapolated using biostratigraphic tie points (Fig. 9).


cycle consists of three paleosols (Fig. 17), in a pattern

that is repeated throughout the upper John Day

Formation (Figs. 3–8) with the exception of the

uppermost parts of the Johnson Canyon and Bone

Creek sections (Figs. 5 and 8). The basal Xaxus

paleosol of each cycle has a deep (>50 cm) calcic

horizon, that is usually thick (15–30 cm), tabular and

restricted to a limited thickness of about 30 cm. This

paleosol is then capped by two Xaxuspa paleosols

with shallow (< 50 cm) calcic horizons, that have

abundant small, rounded nodules (2–15 cm) scattered

through a substantial thickness (50 cm) of rock (Fig.

17). Yapas and Yapaspa pedotypes show similar

alternation, as do Plas and Plaspa pedotypes, but these

latter oscillate around 45 cm rather than 50 cm, and

have smaller nodules, perhaps reflecting a shorter time

for formation. These triplet patterns are similar to the

pattern of rapid termination to humid–warm climate,

and long descent into dry–cold climate seen in

Quaternary paleosols and phytoliths of the Palouse

Loess of Washington (Busacca, 1999; Blinnikov et al.,

2002). The Milankovitch frequencies observed in

Quaternary paleosols are 23, 41 and 100 ka, with

either 100 ka or 41 ka dominant. Estimated times for

formation of Oligocene triplets of a Xaxus and two

Xaxuspa paleosols (Table 3) are consistent with 41–

100 ka duration, but Plas–Plaspa triplets may repre-

sent shorter intervals of 23–41 ka. The radiometrical-

ly dated first 5.1 million years of this sequence (Fig.

9) has 105 Xaxus–Xaxuspa or comparable cycles,

again consistent with Milankovitch scale temporal

change.

Milankovitch scale variation was not seen in the

Hemingfordian beds of Johnson and Bone Creeks,

where a paleoclimatic change is indicated by the

appearance of sparsely to non-calcareous silica-

cemented rhizoconcretions (in Patu pedotype) and

horizons (in Tima and Iscit pedotypes). The genesis

Fig. 17. Detailed section of Xaxus and two Xaxuspa paleosols at

Roundup Flat (Fig. 4; 131–134 m above Picture Gorge tuff in

composite section). Such triplet patterns of paleosols alternate on

Milankovitch time scales.


of such silica-cemented horizons in modern soils has

been studied in southeastern Australia (Chartres and

Norton, 1993) and southwestern US, where they are

called duripans (Chadwick et al., 1987, 1995), in

Mexico where they are known as tepetate (Oleschko,

1990; Flores-Roman et al., 1996) and in Ecuador as

cangahua (Creutzberg et al., 1990). Extensive duri-

pans form in vitric volcanic tuffs, which release

abundant silica during humid weathering (Flores-Ro-

man et al., 1996), and from the activity of sulfur-

reducing bacteria in organic soils (Birnbaum et al.,

1986; Retallack and Alonso-Zarza, 1998). Silicifica-

tion of plant material also occurs in hot springs (Jones

et al., 1998), but the rhizoconcretions of the Hemi-

ngfordian beds do not show cellular permineralization

found in hot springs. Volcanic origin of silcretes in

paleosols of the Hemingfordian beds is unlikely,

because they have smaller amounts of volcanic shards

than underlying paleosols, as an indication of declin-

ing volcanic activity. Furthermore, Hemingfordian

paleosols are surprisingly rich in sodium (soda–potash

ratios more than 1: Figs. 12–14), indicating saliniza-

tion in a paleoclimate much drier than Mexican and

Ecuadorian high-altitude volcanic soils with silica-

cemented layers. The scattered silica is most like opal

and chalcedony of dry and highly seasonal soils in

which highly alkaline groundwater increases silica

dissolution and remobilization (Chadwick et al.,

1987, 1995). Banding in the upper John Day Forma-

tion silcretes (Fig. 18C,D) is evidence of strong

climatic seasonality, probably wet–dry seasonality in

an overall semiarid paleoclimatic regime.

Silica-enriched paleosols of the Hemingfordian

beds (Figs. 5 and 8) are in striking contrast to the

carbonate-nodule-studded Xaxus, Plas and Yapas

paleosols of the rest of the John Day Formation

(Figs. 3–8). In North America today, calcareous

nodules are most abundant in the summer-wet inte-

rior deserts of the Great Plains, Texas, New Mexico

and north-central Mexico (Gile et al., 1981), whereas

duripans and lesser carbonate are found in the

deserts of summer-dry California, Nevada and Ore-

gon (Chadwick et al., 1987, 1995). This distinctive

silica-encrusted paleosol suite may represent the

onset of current summer-dry (Mediterranean) climate

in Oregon at around 19 Ma (Fig. 9), and perhaps its

current extent from California north to central Wash-

ington and east as far as Utah (FAO, 1975a). An

increase in both aridity and seasonality at about this

time is also indicated by oxygen isotopic composi-

tion of equid teeth in central Oregon (Kohn et al.,

2002).

4.2. Paleoflora

The only fossil plants seen in paleosols near

Kimberly and Spray were hackberry endocarps (Cha-

ney, 1925), but these were only abundant in the lower

part of the Johnson Creek section (Fig. 8). Hackberry

endocarps are a biased fossil record because of their

biomineralization, which is unusual for plants (Retal-

lack, 1998). Fossil root traces and rhizoconcretions of

the upper John Day Formation include both stout,

tapering forms and fine filaments, interpreted as roots

of a mix of grasses and trees. Calcareous nodules and

Fig. 18. (A) Crumb structure in type Patu clay loam pedotype (607 m above Picture Gorge tuff), interpreted as evidence for sod grasslands, and

overlying banded silcrete, interpreted as evidence for strong paleoclimatic seasonality in an arid regime (hammer in ellipse for scale); (B–D)

photomicrographs under crossed nicols of (B) crumb ped from type Patu clay loam (JODA8365), (C) banded silica cement from silcrete below

Iscit paleosol at 605 m (JODA8355); (D) silica-replaced fine root trace from type Patu clay loam (JODA8367).


high soda content are also evidence of open, dry

vegetation. Plausible modern analogs are bunch grass-

lands and grassy deciduous forests of the Central

Transmexican Volcanic Belt near Tehuacan (Retallack

et al., 2000).

Janis (2000) has suggested that Oligocene vege-

tation in the Great Plains and western North America

may have been comparable to South African fynbos,

which is a small-leaved shrubland of nutrient-poor

sandy soils on early Paleozoic quartzites of the Cape

Mountains (Pauw and Johnson, 1999). Fynbos is

also comparable to the heath and shrubland of the

Hawkesbury Sandstone around Sydney, Australia

(Beadle, 1981). Oligocene–Miocene volcanic soils

were a different and more fertile substrate (Retallack,

1983; Retallack et al., 2000). Fynbos, heath and

shrublands have common sedges, but few, if any,

grasses or earthworms. In contrast, Oligocene–Mio-

cene paleosols have grass-like root traces, earthworm

trace fossils, granular-crumb ped structure, hackberry

pits (Retallack, 1983; Retallack et al., 2000) and

silica phytoliths of grasses (Stromberg, 2002, this

volume). Furthermore, fynbos has small, sclerophyll,

evergreen leaves, unlike the hackberry (Celtis)

known from Oligocene–Miocene paleosols in Ore-

gon and South Dakota (Chaney, 1925). Oligocene

fossil floras of western North America have revealed

a variety of plant communities (Wing, 1987, 1998),

but nothing as small-leaved or scleromorphic as

fynbos.

Another clue to vegetation of the past comes from

distinctive assemblages of trace fossils, which are


remarkably similar to trace fossil assemblages of the

Quaternary Palouse Loess of Washington state (Tate,

1998; O’Geen and Busacca, 2001). The shallow-

calcic (< 50 cm to Bk), green (Xaxuspa) paleosols

have abundant backfilled burrows of the ichnogenus

Taenidium (Fig. 19F), which were never seen in deep-

calcic (>50 cm to Bk) Xaxus or other deep-calcic

pedotypes. The deep-calcic Xaxus paleosols in con-

trast have trace fossils of Edaphichnium and Pallich-

nus (Fig. 19A–E). This striking alternation of trace

fossil assemblages is found throughout the strati-

graphic range of these trace fossils (Figs. 3–8, 10).

Modern Taenidium in comparable soils and paleosols

of the Palouse region of Washington is constructed by

cicada species (Okanaga vanduziae), which are re-

stricted to sagebrush desert vegetation and which

vanish at the ecotone with grassland (O’Geen and

Busacca, 2001). In contrast, Edaphichnium is the

chimney of earthworms (Bown, 1982; Bown and

Kraus, 1983) and such pelletoidal fabric is diagnostic

of grassland soils and paleosols in Quaternary loess of

eastern Washington (Tate, 1998). Pallichnus is an

ichnogenus of dung beetle boli (Retallack, 1984),

and part of the Coprinisphaera ichnofacies, also

characteristic of grassland soils and paleosols (Retal-

lack, 1990; Genise et al., 2000). Also from a Xaxus

paleosol is Termitichnus, nests of ground-dwelling

termites (Smith et al., 1993), but the Oregon nests

are not elaborate and are found at only one strati-

Fig. 19. Trace fossils of Edaphichnium (A), Pallichnus (B–E) and Taenid

Formation. Localities– specimen numbers are (A) Sorefoot Creek–JODA

Roundup Flat 207.4 m level–JODA8206. All traces are to the same scale

graphic level (Fig. 10). In summary, the trace fossil

assemblages indicate alternation between sagebrush

desert and short desert grassland (Fig. 17), and local

age calibration (Fig. 9) shows that this alternation was

on Milankovitch temporal frequencies.

This alternation of shrubland and desert grassland

changed by 24 Ma during deposition of the upper

John Day Formation to alternation of desert shrubland

and desert scrub. Trace fossils become rare and are

mainly small mammal burrows within the Kimberly

Member, which is silty and loessic. Plas and Plaspa

aleosols in this eolianite facies have shallow calcic

horizons, and weakly pedal soil structure, with little

trace of filamentous root traces like those of grasses

(Fig. 15). The Kimberly Member also has a white to

pink hue different from other parts of the John Day

Formation.

The lower Haystack Valley Member in Balm Creek

has a suite of green (Xaxus and Xaxuspa) and brown

(Yapas and Yapaspa) paleosols like those of the upper

Turtle Cove Member, although darker, more indurated

and less calcareous. This paleosol suite indicates a

more humid, though still semiarid climate, and rever-

sion of vegetation to wooded grassland and desert

shrubland. In the middle Haystack Member of Balm

Creek, Black Bone Hill and Johnson Creek sections,

the eolianite facies with pale paleosols (Plas and

Plaspa) indicates later climatic drying and reappear-

ance of desert scrub.

ium (F) from the Oligocene Turtle Cove Member of the John Day

8343, (B–E) Roundup Flat, 188.6 m level– JODA8177, and (F)

.

G.J. Retallack / Palaeogeography, Palaeoclimat226

Hemingfordian beds of Bone and Johnson Creeks

include a distinctive new suite of paleosols (Figs. 5, 8,

11–14) and distinctive new soil structures (Fig. 18A–

D). Some of these paleosols (Iscit and Patu pedotypes

in Johnson Creek) are the oldest (at 19 Ma) currently

known in Oregon with pervasive crumb peds and fine

networks of mainly filamentous root traces. Such

finely crumb-structured paleosols are the same geo-

logical age in the Great Plains of North America (19

Ma in Anderson Ranch Formation; Retallack, 1997a;

MacFadden and Hunt, 1998; Hunt, 2002). Crumb

structure is found in modern sod grasslands, which

have such a dense root mat that they can be excavated

and rolled up like a carpet for replanting (Retallack,

2001a). This soil structure differs from the fine,

subangular, blocky structure and scattered fine root

traces of presumed bunch grasses in geologically

older paleosols in the John Day Formation (Retallack

et al., 2000), and the North American Great Plains

(Retallack, 1983). Considering also the shallow car-

bonate and silica of associated paleosols, this early

sod formed under short grassland as part of a vege-

tative mosaic including dry woodlands.

The suggested transition from Oligocene bunch

grasslands to Miocene sod grasslands probably in-

volved new species of grasses, because of the very

different climatic regime indicated by paleosols in

Oregon. At present, the summer-dry western grass-

lands of California, Oregon, Washington, Idaho and

Utah are within the western wheat grass (Agropyron

spicatum) province, whereas dry parts of the sum-

mer-wet Great Plains and the northern Mexican

Plateau are within the buffalo grass (Bouteloua

gracilis) province (Leopold and Denton, 1987).

The actual species of grasses involved during the

Miocene and Oligocene are unknown, although such

western steppe taxa as sagebrush (Artemisia),

greasewood (Sarcobatus) and mormon tea (Ephedra)

are evident from pollen records in the western US

well back into the Eocene (Leopold et al., 1992),

and Miocene spread of open-habitat pooids, arundi-

noids and panicoids in the Great Plains is inferred

from phytoliths (Stromberg, this volume). Hemi-

ngfordian mammals of Oregon and the Great Plains

are largely different species, but these faunas share

many genera (Rensberger, 1973, 1983; Dingus,

1990; Woodburne and Robinson, 1977; Coombs et

al., 2001).

4.3. Paleofauna

In addition to insect and earthworm trace fossils

characteristic of particular plant communities, fossil

mammal bone, turtle scute and snail shell are common

within the upper John Day Formation, especially

within large (>20 cm diameter) paleosol nodules in

a form of preservation very similar to that documented

by Downing and Park (1998). Mammalian faunas

changed considerably with changes in paleoclimate

and vegetation during the late Oligocene and early

Miocene (Fig. 10), which was a period of marked

modernization in ungulates (Janis, 2000) and grass

phytoliths (Stromberg, this volume). Oreodont-domi-

nated faunas persisted throughout the Turtle Cove

Member, for which limited spatial and temporal

variation of habitat is indicated by dominance of green

Xaxus and Xaxuspa paleosols (Figs. 3 and 4). The

gracile oreodont Eporeodon occidentalis, three-toed

horses (Mesohippus spp., Miohippus spp.) and rhinos

(Diceratherium spp.) are common throughout the

lower and middle Turtle Cove Member (Fremd,

1988, 1991, 1993; Fremd et al., 1994). The rhinos

are hypsodont and so presumed grazers, but the horses

are not hypsodont. Nevertheless, microwear studies

indicate substantial amounts of abrasive grass in

Oligocene horse diets (Solounias and Semprebon,

2002). There also are common fossil tortoises (Hay,

1908), and a diverse assemblage of fossil land snails

(Hanna, 1920, 1922; Pilsbry, 1939–48; Roth, 1986;

Pierce, 1992).

Climatic change to arid conditions with muted

variation at about 25.8 Ma (Fig. 16) coincides with

the first appearance of hoglike oreodonts (Meryco-

ochoerus superbus; Lander, 1998) and of pocket

gophers (Entoptychus spp.; Rensberger, 1971). This

also is the beginning of the ‘‘cat gap’’ (Van Valken-

burgh, 1991) and ‘‘entelodont gap’’ (Foss and Fremd,

2001), a period of some 7 million years when there

were no nimravids, felids, or entelodonts in North

America. These taxa re-entered North America, prob-

ably from Europe, during the Hemingfordian (18.8

Ma according to MacFadden and Hunt, 1998). Faunal

overturn at 25.8 Ma is the basis for division of the

Arikareean NALMA into ‘‘Monroecreekian’’, then

‘‘Harrisonian’’ (Alroy, 2000).

Fossils remain common in green calcareous (Xaxus

and Xaxuspa) paleosols after this faunal overturn at

ology, Palaeoecology 207 (2004) 203–237


about 25.8 Ma. When the last of these green paleosols,

dated at about 24.5 Ma (Fig. 5), is covered by a

sequence of pinkish-white calcareous (Plas and

Plaspa) paleosols of drier inferred paleoclimate of the

Kimberly Member, bones become rare (Fig. 16).

Merycochoerus, Miohippus and Diceratherium per-

sist, but the common mouse deer species Hypertragu-

lus hesperius is replaced by a smaller species

Hypertragulus minutus (Webb, 1998). Pocket gophers

(E. planifrons and E. individens) evolved to larger size,

greater hypsodonty and more marked fossorial adap-

tations (Korth, 1994), and fossil rodent burrows are

common in the paleosols. Many of the rodent burrows

are nuclei of carbonate nodules, which are gray with

organic matter and manganese, as if encrusted with

roots and algae, like comparable burrows in the

Harrison Formation of Nebraska (Retallack, 1990).

In contrast, Xaxus paleosol nodules and nodularized

burrows have less carbon than their matrix, and their

orange micrite contrasts with the gray-green clayey

matrix. No large tortoises or snails were found in the

Kimberly Member, perhaps because of desertification

indicated by the shallow depth to carbonate in the

paleosols (Fig. 16).

Return of more humid and grassy vegetation in-

ferred from green (Xaxus and Xaxuspa) and brown

(Yapas and Yapaspa) paleosols in the early Miocene

lower Haystack Member of Balm Creek is within the

youngest of the entoptychine zones (E. individens:

Rensberger, 1971), where there is a new fauna of

oreodons (Merychyus arenarum), and camels (‘‘Para-

atylopus’’ cameloides: Fremd et al., 1994).

Within Hemingfordian beds with aridland paleo-

sols (Plas and Plaspa) of Black Bone Hill, Johnson

and Bone Creeks, the mammal fauna is again changed

(Coombs, 1978; Fremd et al., 1994; Lander, 1998;

MacFadden, 1998; Webb, 1998; Coombs et al.,

2001). The fauna now has very different rodents

(Mylagaulodon, Schizodontomys) and is dominated

by hypsodont horses (Parahippus) and camels (Gen-

ntilicamelus, ‘‘Paratylopus’’), rather than oreodonts

(Fig. 10). This is the beginning of the Miocene

grazing guild of wooded grasslands, which reached

its greatest diversity by about 10–15 Ma (Webb,

1998; Janis et al., 2002). Unfortunately, fossils are

known mainly from paleochannels, rather than from

paleosols (Coombs et al., 2001), but the appearance

of sod grassland paleosols (Iscit and Patu) is compat-

ible with the mammalian ecological shift toward

grazing.

4.4. Paleotopography

Paleocurrents (Fig. 11) and paleosol distribution

are evidence of a broad northwest-flowing river basin

during deposition of the upper John Day Formation.

The wide extent of this alluvial lowland is revealed

by muted lateral thickness variation of volcanic ashes

within the Turtle Cove Formation. The current loca-

tion of Longview Ranch was near the eastern margin

of the seasonally inundated floodplain, represented

by green unoxidized (Xaxus) paleosols. Evidence for

this comes from observations 5 km to the northeast

in Rudio Canyon at the same stratigraphic interval of

ash-flow tuff H, where there is a sequence of red,

clayey (Luca) paleosols of well-drained interfluves

(Retallack et al., 2000). The paleoslope 100 km to

the west into the current area of the Painted Hills was

more gentle, because only a few green, poorly

drained (Xaxus) paleosols are found there, along

with brown, lowland, moderately drained (Maqas

and Yapas) paleosols (Retallack et al., 2000). To

the west were eroded hills of a moribund volcanic

arc, which was active in Eocene time. This whole

region was an Oligocene and Miocene back-arc basin

to the ancestral Cascades volcanic arc (Retallack et

al., 2000).

Considerable local topography was generated by

paleovalleys preserved within the Haystack Valley

Member. These erosional episodes do not appear to

be related to tectonic uplift, local doming or fault-

ing, because they are concordant with successive

thick flows of the Columbia River Basalt Group

(Fisher and Rensberger, 1972). Local doming and

faulting postdated these flood basalts, and was

coeval with middle Miocene accumulation of the

Mascall Formation, as can be seen from sedimentary

onlap of that formation south of Picture Gorge

(Retallack et al., 2002). Valley-cutting events at

23.2, 21.1 and 19.2 Ma were the culmination of

climatic cooling and drying trends, as revealed by

declining depth to carbonate in paleosols (Fig. 16).

The Hemingfordian beds of Bone Creek also show

an upward drying cycle, terminating with a thick

duripan (618 m in Fig. 5) probably about 17 Ma in

age (Fig. 9).

limatology, Palaeoecology 207 (2004) 203–237

4.5. Paleosol parent materials

Paleosols of the upper John Day Formation formed

largely on redeposited rhyodacitic volcanic ash,

which varies little in chemical or mineral composi-

tion (Retallack et al., 2002). Volcanic shards are

common, and chemical analyses indicate that the

paleosols were little altered from their parent mate-

rial (Bestland, 2000). Some of the paleosols formed

directly on fresh volcanic airfall ash, which remains

as the Deep Creek, Biotite, Tin Roof and ATR tuffs

(Fig. 8). Most paleosols were formed on ash that fell

elsewhere, weathered to some extent, then mixed and

redeposited by wind and water. Rock fragments

include mainly rhyodacite, but also rare basalt, schist

and granite. Volcanic shards are rare, and rock frag-

ments much more common in the Hemingfordian

beds than in the rest of the John Day Formation,

perhaps due to deposition in valleys eroded into the

underlying rocks and to declining rate of tuffaceous

volcanism.

G.J. Retallack / Palaeogeography, Palaeoc228

5. Discussion

Late Oligocene and early Miocene was a time of

profound fluctuation in paleoclimate, when the Ant-

arctic ice cap was established and expanded for the

first time to near sea level (Zachos et al., 2001a). It

was also a time of evolutionary radiation for plants

(Jacobs et al., 1999) and mammals of grasslands

(MacFadden, 2000). The Upper John Day Formation

paleosol sequence is a high-resolution record of

these climatic and biotic events (Table 3; Figs. 20

and 21).

5.1. Oligo–Miocene climatic events

Paleosols of the upper John Day Formation ex-

posed on Longview Ranch are a paleoclimatic ar-

chive that in places is superior to that of deep-sea

cores. The most complete deep sea record of late

Oligocene climate record from the oxygen isotopic

composition of foraminifera had to be spliced togeth-

er from several cores because of core recovery

problems, then tuned to orbital cyclicity and still

some climatic beats are missing (Zachos et al.,

2001b). The upper Turtle Cove and lower Kimberly

Members of the John Day Formation, however, are

unlikely to be missing a single 100 ka beat in an

untuned record of 105 paleoclimatic cycles within the

5.1 million year duration of these rocks (Figs. 3–5).

The upper Kimberly and Haystack Valley Members

appear comparably complete within their measured

sections (Figs. 6–8), but less securely dated, and

there may be disconformities between measured

sections. These rocks crop out in extensive large

badlands with ample lateral exposure of each paleo-

climatic cycle. Large amplitude cycles in oxygen

isotopic composition of marine foraminifera (Zachos

et al., 2001a) are found at the same time as large

amplitude cycles in paleosol carbonate depth in

Oregon (Fig. 16), and small amplitude cycles are

found in both during intervening times. One of these

times of low amplitude climatic fluctuation was at the

Oligocene–Miocene boundary (23.2 Ma) and the

other was within the late Oligocene (25.8 Ma). Both

were times of arid climate indicated by paleosols

(Fig. 16), and the paleoclimatic shift had profound

effects on fossil mammals in central Oregon (Fremd

et al., 1994; Hunt and Stepleton, 2001). Both were

also times of Antarctic ice expansion, revealed by ice

rafted debris in deep sea cores (Zachos et al., 2001a).

An especially profound paleoclimatic change at

about 19 Ma is recorded in the Johnson Creek

section. Before that time most paleosols had large

calcareous nodules, like paleosols common through-

out the Cenozoic in the Great Plains of North

America. After that time, large carbonate nodules

are uncommon, with carbonate limited to partial

cementation of chalcedony-encrusted root traces.

Hemingfordian paleosols of Bone and Johnson

Creeks had natric (soda rich) clays and banded,

botryoidal and mammillar silcrete, like that at the

top of the Harrison Formation in Nebraska (Retal-

lack, 1997a). Hemingfordian silcretes of Bone and

Johnson Creeks are most like those now found in

arid Nevada and California (Chadwick et al., 1987,

1995). The Great Plains now has a climate with

summer rain fed by monsoon-like circulation of

warm air masses from the Gulf of Mexico. The

Pacific Northwest, however, has long dry summers

because of cool, high-pressure air masses generated

by cold ocean currents moving south from Alaska.

This is a fundamental difference between climates

of the two regions. The Pacific Northwest has a

Fig. 20. A reconstruction of Longview Ranch during Late Oligocene (late Arikareean) deposition of the Kimberly Member of the upper John

Day Formation. Soil column lithological symbols are as for Fig. 3.


xeric moisture regime, whereas the Great Plains is

ustic (following terminology of Soil Survey Staff,

1999). The early Miocene may have been not only

a dry phase following the aridity of the Oligocene–

Miocene boundary, but also a regional transition

between Oligocene ustic moisture regimes and Mio-

cene to modern xeric moisture regimes. Such differ-

ences in available summer moisture would have led

to substantial changes in vegetation, and in the

capacity of vegetation to mitigate soil erosion.

5.2. Early Miocene advent of short sod grassland

Crumb-structured paleosols (Patu and Iscit) of

the Hemingfordian beds (early Miocene, ca. 19

Ma) in Johnson Creek are the geologically oldest,

Fig. 21. A reconstruction of Longview Ranch during early Miocene (Hemingfordian) deposition of the Rose Creek Member of the upper John

Day Formation. Soil column lithological symbols are as for Fig. 3.


likely sod grassland paleosols (Mollisols) currently

known in Oregon (Retallack, 1997a). The silica and

shallow carbonate horizons of these paleosols are

evidence for a dry climate (< 400 mm mean annual

precipitation). This and the shallow fossilized root-

ing depth indicates that these were short grasslands.

Similar evidence from North American paleosols

indicates that early and middle Miocene grasslands

were confined to semiarid regions until the advent

of Mollisols with deep calcic horizons at about 7

Ma, representing the earliest tall grasslands (Retal-

lack, 1997a, 2001a; Retallack et al., 2002).

An early Miocene age of short sod grasslands in

Oregon is compatible with increased abundance of

grass pollen in rocks of that age in the Pacific

Northwest (Leopold et al., 1992). Phytoliths of

open-habitat grasses become more abundant at this

time in the Great Plains (Stromberg, 2002, this

volume), but have not yet been studied in Oregon.

Sod grassland interpretation is also compatible with a

continent-wide adaptive radiation of hypsodont para-

hippine horses (MacFadden and Hulbert, 1988),

known to have been grazers from tooth morphology

and wear (MacFadden, 2000; Janis et al., 2002;


Solounias and Semprebon, 2002). The new grazing

fauna of parahippine horses is also known in Hemi-

ngfordian rocks of Oregon (Woodburne and Robin-

son, 1977).

The first appearance of sod grasslands in Oregon

at 19 Ma is associated with dry climate, but the

grassland paleosols are stratigraphically higher than

desertic paleosols (Plas and Plaspa) and below sil-

crete paleosols of wetter climate higher in the

sequence (Figs. 5 and 8). Within the paleosol se-

quence of the Great Plains, the earliest sod grassland

paleosols of the basal Anderson Ranch Formation,

also now dated at 19 Ma (MacFadden and Hunt,

1998), are above desertic shallow-calcic paleosols of

the upper Harrison Formation (Eagle Crags locality;

Retallack, 1990), and among deeper calcic paleosols

of the Anderson Ranch Formation (Agate locality;

Retallack, 1997a). Both Oregon and Great Plains

sequences were coeval with a wet paleoclimatic

inflection, with summer-dry seasonality in Oregon

and summer-wet seasonality in Nebraska. This was

one of numerous wet–dry cycles (Schultz and Stout,

1981; Martin, 1994), and it is unclear why this

particular sequence of the early Hemingfordian (19

Ma), and not earlier or later paleoclimate cycles, was

the one to introduce sod grasslands. Such climatic

volatility is on time scales shorter than likely oro-

graphic development of rain shadows (Kohn et al.,

2002), although these would exacerbate local climat-

ic variation. Neither the 19 nor 17 Ma arid phases

were as dry as the one at the Oligocene–Miocene

boundary (23.2 Ma), judging from the Great Plains

paleosol record (Retallack, 1997a). Thus, it seems

unlikely that climatic drying or seasonality by itself

introduced grasslands.

Other explanations for grassland origins have in-

cluded lower atmospheric carbon dioxide, thus favor-

ing plants with C4 photosynthetic pathways such as

tropical grasses (Cerling et al., 1997). However,

carbon isotopic studies of fossil grasses and grazers

indicate that early grasslands in both tropical and

temperate regions were mostly C3 before 3 Ma in

the Great Plains (Fox and Koch, 2003, this volume),

but before 7 Ma elsewhere (MacFadden, 2000). The

lack of global synchroneity in expansion of C4 grass-

lands argues for local rather than global atmospheric

causes (Fox and Koch, 2003). Fire is a physical force

promoting grasslands, because trees are destroyed by

fire, but grasses sprout again from undamaged rhi-

zomes (Vogl, 1974). However, no charcoal was seen

in early Miocene paleosols of either Nebraska or

Oregon, despite its abundance in Miocene paleosols

elsewhere (Retallack, 1991; Morley and Richards,

1993). Broad plains have been thought to promote

grasslands by allowing the free movement of fire and

herds of ungulates, but both the Great Plains and

Oregon sequences were extensively dissected by ero-

sional valleys during the early Miocene, compared

with laterally extensive volcanic ashes and sedimen-

tary facies in underlying Oligocene rocks (Retallack,

1983; Retallack et al., 2000).

The explanation favored here for the origin of

this new ecosystem is grass-grazer coevolution, as

suggested by Kowalesvsky (1873). Grasses with

their modular, rhizomatous growth, basal leaf mer-

istems, sheathing leaves and protected terminal

meristems are better adapted than other plants at

withstanding the grazing pressure of large herds of

ungulates. Horses and antelope, on the other hand,

are uniquely suited by virtue of their high crowned

teeth, hooves and elongate limbs to life on the open

plains. Large herbivores such as rhinos and ele-

phants are particularly destructive of trees, stripping

their bark and toppling their trunks (Retallack,

2001a). By this view, grassland sod evolved as a

group of adaptations in roots and shoots to with-

stand increasingly effective trampling and grazing

by mammals. Against a near-chaotic background of

mountain uplift, sea level change and paleoclimatic

oscillation, sod–grassland ecosystems appeared and

stayed in semiarid regions of Oregon.

Acknowledgements

I thank Russell Hunt, Jonathan Wynn, Nathan

Sheldon, Ted Fremd, Chris Schierup, Lia Vella and

Scott Foss for assistance during fieldwork, preparation

and curation of the fossil collections. Scott Bates,

Dave Van Cleve and Rob Williams generously gave

permissions and accommodation for our work on

Longview Ranch. Finally, Caroline Stromberg drew

together the small circle of those interested in ancient

grasslands at a symposium in Berkeley in 2001, and

diligently edited this manuscript. Work was funded by

NSF grant EAR 0000953.

Appendix A

New chemical analyses of paleosols of the upper John Day Formation

Pedon Hz m JD no. SiO2 TiO2 Al2O3 FeO Fe2�O3 MnO MgO CaO Na2O K2O P2O5 LOI Total g cm� 3 Ba Nb Rb Sr Zr

Tima A 623.9 8383 55.57 0.92 13.22 0.32 5.94 0.03 1.42 2.05 1.33 1.19 0.07 17.36 99.53 1.66 268 8 57 184 187

Bn 623.7 8384 56.73 0.97 13.49 0.32 5.96 0.03 1.54 2.15 1.30 1.05 0.07 15.86 99.60 1.67 322 11 56 203 194

Bn 623.5 8385 55.11 1.00 13.43 0.32 6.01 0.03 1.53 2.29 1.38 1.07 0.08 16.89 99.25 1.59 315 21 54 215 186

C 623.2 8386 55.69 1.00 13.89 0.39 5.28 0.04 1.63 2.79 1.50 1.13 0.14 15.40 99.01 1.6 350 14 55 256 194

Tima Bq 623.0 8387 56.81 0.94 13.89 0.45 4.24 0.09 1.42 2.55 1.62 1.35 0.10 15.26 98.86 1.59 388 23 61 248 217

Tima Bq 621.5 8388 57.85 0.81 13.64 0.32 4.10 0.04 1.23 2.36 1.63 1.23 0 15.83 99.21 1.59 327 17 60 237 239

Iscit A 620.3 8354 58.79 0.91 13.51 0.26 5.46 0.04 0.9 1.38 0.57 0.86 0.06 16.79 99.61 1.4 227 18 58 83 243

Bq 620.1 8355 60.85 0.71 12.97 0.26 4.02 0.03 0.94 1.40 0.84 1.21 0.06 15.90 99.29 1.58 302 11 63 99 187

Bq 620.0 8356 61.11 0.73 13.04 0.39 4.09 0.04 0.92 1.59 0.97 1.31 0.06 14.73 99.10 1.72 326 22 63 127 197

Patu A 619.9 8357 56.00 0.68 13.05 0.26 4.09 0.03 1.24 1.58 0.88 1.11 0.05 19.46 98.54 1.68 283 15 56 119 179

A 619.8 8358 57.39 0.71 13.83 0.32 4.08 0.04 1.40 1.74 0.94 1.07 0.05 17.33 99.00 1.66 261 17 60 130 188

Bk 619.6 8359 56.27 0.72 13.06 0.39 4.12 0.04 1.25 1.66 1.01 1.24 0.06 18.09 98.06 1.63 318 14 60 130 200

C 619.3 8360 56.98 0.71 13.24 0.32 4.12 0.04 1.32 1.75 1.06 1.30 0.07 18.15 99.18 1.65 290 21 66 140 219

Tima Bn 613.6 8378 53.72 0.88 14.41 0.19 5.47 0.04 1.32 2.26 1.43 1.35 0.05 17.77 99.00 1.85 330 13 66 213 208

Patu A 612.5 8364 56.32 0.86 13.24 0.13 6.45 0.05 1.34 1.64 0.96 1.30 0.05 16.98 99.42 1.66 423 19 64 121 195

A 612.4 8365 55.12 0.95 13.74 0.13 6.95 0.04 1.32 1.78 1.09 1.43 0.05 16.47 99.18 1.66 446 15 68 145 204

Bk 612.3 8366 55.24 0.89 13.79 0.19 6.75 0.04 1.42 1.82 0.90 1.34 0.05 16.64 99.18 1.62 428 15 68 137 206

C 612.2 8367 67.09 0.41 8.85 0.13 3.67 0.02 0.89 1.14 0.46 0.77 0.04 15.62 99.16 1.38 277 10 53 68 135

Abi. A 612.1 8368 55.59 0.93 13.67 0.45 5.43 0.05 1.15 2.33 1.65 1.82 0.08 15.32 98.64 1.63 691 12 76 218 188

C 612.0 8369 57.02 0.94 13.91 0.39 5.19 0.06 1.17 2.38 1.59 1.74 0.09 14.11 98.76 1.64 751 19 76 233 201

C 611.8 8370 62.72 0.50 10.53 0.19 4.35 0.03 1.24 1.25 0.55 0.91 0.03 15.94 98.32 1.58 243 15 62 76 156

Patu A 611.0 8371 56.86 0.84 13.56 0.39 5.94 0.06 1.36 2.56 1.64 1.74 0.06 13.80 99.00 1.71 888 12 70 263 205

A 610.8 8372 57.50 0.87 13.46 0.45 4.97 0.05 1.30 2.62 1.77 1.83 0.06 13.80 98.89 1.7 891 16 73 272 209

Bk 610.6 8373 56.59 0.82 13.27 0.45 5.55 0.05 1.27 2.58 1.75 1.77 0.06 14.73 99.08 1.71 891 18 71 259 201

C 610.3 8374 57.60 0.91 13.92 0.58 3.79 0.06 1.11 3.13 2.13 1.83 0.17 13.37 98.81 1.71 871 20 78 297 204

Cmti A 610.0 8375 54.29 0.85 12.74 0.19 6.76 0.05 1.74 2.62 1.27 1.57 0.20 16.52 98.98 1.63 968 14 65 276 199

C 609.8 8376 53.86 0.81 13.07 0.26 6.26 0.05 1.63 3.17 1.48 1.68 0.53 15.95 98.94 1.66 972 10 71 255 197

Tima Bn 583.5 9074 51.47 0.89 15.49 0.26 6.22 0.03 1.39 1.64 0.71 0.94 0.03 19.28 98.46 2.08 278 10 59 125 203

Tima Bn 573.3 9072 57.53 0.79 13.24 0.45 3.88 0.06 1.30 2.70 1.28 1.45 0.35 16.39 99.58 1.67 427 13 64 225 194

Tima Bn 569.2 9070 54.59 1.04 15.34 0.45 5.05 0.07 1.17 2.56 1.68 1.14 0.05 16.82 100.11 1.88 426 11 50 249 226

Tima Bn 552 9069 54.02 0.83 14.66 0.26 5.62 0.08 1.52 2.30 1.30 1.09 0.16 18.49 100.43 1.89 262 13 55 185 247

Tima Bn 545.3 9067 53.80 0.98 14.34 0.32 6.89 0.07 1.68 2.67 1.85 1.16 0.08 15.80 99.77 1.88 347 10 49 235 195

Plas AB 537.6 9066 59.22 0.82 13.99 0.51 4.61 0.07 1.19 2.56 1.95 1.62 0.11 13.18 100.00 1.74 438 16 69 234 198

Plas AB 526.3 9065 59.80 0.82 13.98 0.64 4.61 0.11 1.11 3.17 2.03 1.86 0.45 11.23 100.00 1.76 560 16 72 249 194

Plas AB 516.2 9064 58.59 0.80 13.73 0.71 4.53 0.10 1.27 2.45 1.96 1.75 0.09 13.21 99.38 1.74 498 11 70 209 207

Plas AB 502.3 9063 59.56 0.79 13.43 0.71 4.51 0.08 1.36 2.56 2.25 1.86 0.22 12.62 100.14 1.74 546 13 71 187 199

Plas AB 495 9088 57.94 0.80 13.05 0.64 5.04 0.11 1.31 2.82 2.06 1.75 0.16 13.17 99.00 1.73 441 15 70 199 193

Plas AB 482.7 9087 58.71 0.90 14.15 0.84 5.35 0.12 1.19 3.09 2.23 1.99 0.12 10.40 99.29 1.78 537 7 74 238 192

Plas AB 471.3 9086 60.97 0.78 14.00 0.71 4.16 0.08 1.22 2.88 2.29 1.89 0.22 10.93 100.30 1.71 449 13 71 228 209

Plas AB 447.4 9084 56.15 0.90 13.63 0.68 4.75 0.08 2.62 2.42 2.92 1.63 0.09 14.37 100.45 1.76 400 12 60 191 208

Plas AB 432.6 9083 54.72 0.89 13.31 0.51 5.14 0.07 1.84 2.51 3.11 1.66 0.09 15.61 99.60 1.64 330 15 70 159 216

Plas AB 421.2 9082 56.24 0.86 13.46 0.71 5.00 0.08 1.83 2.99 2.75 1.74 0.13 13.56 99.54 1.71 366 17 75 180 215

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Plas AB 411.2 9081 57.51 0.76 13.91 0.64 4.18 0.10 1.70 2.07 2.97 1.72 0.06 13.85 99.64 1.92 431 15 78 184 240

Plas AB 398.8 9080 56.80 0.92 13.73 1.09 5.21 0.10 1.82 3.13 3.15 1.48 0.24 12.66 100.56 1.86 420 10 64 189 200

Xaxus AB 387.4 9079 56.53 0.83 13.05 0.71 5.46 0.11 1.96 2.32 2.68 1.65 0.12 14.35 99.93 1.88 338 14 63 145 192

Yapas AB 373.6 9078 55.70 0.90 14.08 0.06 6.30 0.09 1.29 2.67 3.59 1.47 0.08 13.40 99.74 1.84 468 11 60 261 223

Yapas AB 357.5 9077 56.52 0.72 13.41 0.39 4.66 0.07 0.95 2.17 3.95 2.42 0.10 14.96 100.44 1.91 412 14 90 184 195

Xaxus AB 344.6 9076 61.61 0.48 11.73 0.51 3.51 0.05 0.86 2.16 3.38 2.16 0.11 12.74 99.50 2.05 254 15 70 179 117

Xaxus AB 334.8 9075 61.50 0.61 11.37 0.61 3.22 0.06 0.79 3.15 3.43 1.66 0.11 12.69 99.31 2.08 371 13 67 199 168

Yapas AB 321.9 9192 56.99 0.77 13.21 0.77 4.77 0.08 1.33 2.86 1.88 1.74 0.25 13.21 98.04 1.82 429 11 68 182 188

Plas AB 311.5 9191 56.53 0.77 13.02 0.77 4.96 0.12 1.56 2.68 1.70 1.61 0.16 15.43 99.49 1.81 425 9 56 166 193

Plas AB 297.6 9190 58.71 0.78 14.17 0.64 5.3 0.09 1.24 3.05 2.21 1.83 0.07 11.26 99.52 1.81 518 11 73 227 212

Plas AB 282.2 9189 58.85 0.83 13.95 0.58 4.95 0.10 1.59 3.21 2.25 1.35 0.16 11.94 99.92 1.74 441 11 61 211 197

Pla’pa A 276.7 8396 55.96 0.83 12.66 0.51 5.36 0.16 1.77 3.24 1.88 1.38 0.33 14.86 99.10 1.76 462 17 60 200 188

A 276.5 8397 57.83 0.86 13.13 0.64 4.56 0.14 1.66 3.19 1.98 1.55 0.33 13.31 99.33 1.75 456 15 63 204 199

A 276.4 8398 56.85 85 12.89 0.58 4.97 0.25 1.71 3.28 1.97 1.46 0.34 14.10 99.41 2.36 503 20 64 204 197

Bk 276.2 8399 33.28 0.45 6.52 0.71 3.96 0.2 1.05 24.9 1.23 1.19 0.18 25.44 99.28 1.72 260 5 29 130 86

Plas A 276.1 8400 55.83 0.84 12.64 0.64 5.40 0.11 1.75 2.97 1.83 1.43 0.17 15.29 99.06 1.69 422 18 61 189 188

A 276.0 8401 57.61 0.87 13.10 0.58 4.67 0.11 1.73 3.19 1.89 1.47 0.20 14.13 99.72 1.71 468 18 67 197 195

A 275.8 8402 57.35 0.86 12.98 0.51 4.50 0.1 1.65 3.31 1.88 1.48 0.26 14.24 99.30 1.71 457 17 64 200 195

A 275.7 8403 55.45 0.84 12.62 0.64 4.75 0.09 1.69 3.21 1.81 1.4 0.22 16.22 99.10 1.68 420 13 56 191 187

Bk 275.6 8404 31.81 0.41 6.20 0.58 4.27 0.44 0.99 26.0 1.13 1.27 0.29 25.95 99.45 1.41 333 5 5 5 5

Pla’pa A 275.4 8405 54.96 0.81 12.45 0.58 4.46 0.1 1.66 3.01 1.87 1.47 0.24 17.55 99.32 1.69 448 8 59 192 189

Plas AB 268.6 8394 54.20 0.87 12.74 0.39 5.93 0.08 2.23 3.01 1.65 1.09 0.11 16.64 99.08 1.79 349 12 51 176 169

Plas AB 259.5 8393 54.48 0.84 13.39 0.32 5.88 0.09 2.12 3.48 1.81 1.16 0.12 15.24 99.04 1.77 329 13 58 189 163

Plas AB 249.5 8392 54.45 0.78 12.66 0.32 5.84 0.09 2.11 2.84 1.67 1.09 0.07 17.69 99.73 1.87 312 16 60 154 207

Plas AB 240.8 8391 55.18 0.88 12.98 0.39 5.86 0.08 1.92 3.11 1.99 0.99 0.1 15.66 99.25 1.79 331 15 50 173 193

Tuff – 229.5 8389 56.03 0.99 13.35 0.00 4.51 0.06 1.93 3.55 1.84 1.38 0.2 14.90 98.87 1.83 667 13 55 314 180

Xaxus AB 219.5 8423 56.76 0.79 13.28 0.71 5.23 0.07 1.62 3.17 2.47 2.51 0.3 12.37 99.50 2.15 651 13 91 390 206

Xaxus AB 206.0 8422 56.21 0.82 13.03 0.51 5.54 0.1 1.73 3.43 2.78 1.81 0.13 12.95 99.20 1.99 461 13 57 300 195

Ya’pa AB 191.0 8421 55.44 1.03 13.46 0.96 5.97 0.11 1.88 3.72 2.74 1.90 0.14 11.86 99.42 2.02 461 10 71 289 178

TRT – 178.0 8407 60.27 0.41 12.20 0.32 3.28 0.06 0.82 2.36 3.69 1.86 0.14 13.25 98.81 1.74 510 17 59 256 223

Xaxus AB 165.0 8419 57.56 0.81 11.69 0.58 5.88 0.09 1.45 3.05 3.05 1.82 0.13 12.95 99.19 2.04 357 10 59 191 161

Xa’pa AB 147.6 8418 55.52 1.01 13.15 1.03 6.42 0.13 1.79 3.84 2.85 1.52 0.20 12.61 100.26 2.13 372 8 50 209 170

Xaxus AB 147.0 8417 56.61 0.89 13.19 0.84 5.83 0.11 1.61 3.50 2.99 1.42 0.09 12.65 99.92 2.06 397 10 49 214 216

Xaxus AB 130.6 8416 56.57 0.98 12.85 1.09 6.40 0.16 1.74 3.67 3.12 1.76 0.10 10.94 99.58 2.06 354 11 60 209 169

Xa’pa AB 113.0 8415 58.92 0.79 12.51 0.84 4.92 0.11 1.14 3.18 3.22 1.87 0.09 11.45 99.24 2.05 467 11 81 219 168

Xa’pa AB 99.0 8410 51.57 0.79 11.41 0.84 4.40 0.23 1.24 7.93 3.07 1.47 0.25 15.62 99.00 2.01 409 10 56 198 153

Xaxus AB 88.0 8409 55.78 1.01 13.22 0.77 6.66 0.15 1.83 3.86 2.82 1.52 0.16 11.25 99.20 2.08 411 14 60 213 200

Xaxus AB 68.0 8408 56.25 1.05 13.64 1.16 6.34 0.16 1.91 3.54 2.69 2.06 0.11 10.48 99.63 2.14 432 14 73 201 225

DCT – 65.0 8406 61.58 0.14 12.10 0.13 2.22 0.05 0.32 2.54 3.81 0.65 0.03 15.83 99.54 1.52 556 63 42 162 393

Xaxus AB 54.5 8431 56.87 0.86 13.14 0.84 5.59 0.12 1.43 2.91 2.75 2.29 0.09 12.69 99.77 2.1 526 13 81 193 217

Xaxus AB 43.5 8429 57.79 0.75 13.17 0.51 4.91 0.09 1.27 2.83 3.26 1.77 0.13 13.72 100.36 2.08 451 18 62 185 222

Xaxus AB 34.5 8428 54.72 0.88 13.26 0.58 5.53 0.10 1.48 3.41 2.82 1.53 0.37 14.43 99.25 2.13 432 18 55 188 199

Xaxus AB 24.0 8427 55.01 0.91 12.90 0.71 5.79 0.19 1.65 3.15 2.72 2.17 0.17 13.43 98.99 2.12 537 14 78 198 222

Xaxus AB 13.0 8426 57.16 0.85 13.28 0.64 5.64 0.12 1.52 2.98 2.91 2.10 0.11 12.70 100.20 1.96 548 18 74 188 223

Error F 1j – – 0.77 .044 0.23 – 0.20 .001 0.04 0.04 0.05 0.02 .015 – – 0.07 50 3 7 0.6 0.6

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Late Oligocene bunch grassland and early Miocene sod grassland ...€¦ · different times. Cursoriality appears in the North American fossil mammal record by early Oligocene (33